Tourists are not allowed to cross the U.S.-Mexico border with more than 5 DVDs.

You also can't bring in more than 20 music CDs, 1 CD player, 1 cell phone, or 12 rolls of unused film. You also have to declare all of these personal effects before entering the country. Otherwise you will be accused of attempted smuggling, and will have your contraband confiscated. Also regulations in Mexico prohibit the importation of used clothes and textiles, so if you want to donate clothes, you should probably do it back at home.

There are A LOT of other rules about what you can and can't bring over the Mexican border.